Still a mystery bantam (to me)

This is the only one out of the 15 assorted, that I have no clue what it could be
He is about three weeks old. He is not the same color as the two other black cochin babies (they are black with white on their chest)
Is he even a cochin to begin with? and if so, what color?
I have stared and looked up all the birds that Ideal has to offer and I am stumped.
Thanks for any help or ideas, or leads.

Golly, except for his color, I'd say Cochin. The color doesn't seem to be black or partridge, either one. Hopefully, someone can help you with this little guy--and it does seem to be a "guy" in those pics.

Knowing the Ideal inventory fairly well, I would say that you have a either a Partridge Cochin or a Brown Red D'Uccle (which often have vulture hocks-- much more commonly than Cochins). However, I don't see the typical beard that D'Uccles would start to exhibit by this age......

Certain breeds are much slower to develop than others..... I have raised over 60+ chicken breeds so far and am always amazed at the differences in development amongst certain breeds. Larger or heavier bodied ones (even amongst bantams) often take longer. This would probably indicate this chick to be a Cochin as I find D'Uccles to develop faster than Cochins.

It's really interesting- to me at least-- how different behaviour is amongst breeds from the hatching experience. I find Seramas especially are precocious. They practically jump right out of the egg and start strutting their stuff, while some of the standards, notably my Penedesencas, are kind of slow and seem exhausted by the process of emerging into the world.....

The 2 D'uccles and the 2 Partridge cochins have their teenage feathers also coming in really good. The D'uccles are already getting spots!
I wish it were a lemon blue, as Illia suggested (except a black version), I looked those up and they are beautiful!